Bioadsorbtion of Arsenic by Prepared and Commercial Crab Shell Chitosan

The present research investigated the arsenic removal performance of prepared and commercial crab shell chitosan by adsorption filtration method. The ability of chitosan to remove arsenic from prepared arsenic contaminated solution was examined by Atomic Absorption Spectrometry (AAS). It is found that the saturation volume of prepared chitosan for l0 mg L-1 As3+/As5+ solution was 8.55 L and its arsenic removal capacity was 6244.2 mg kg-1. For commercial chitosan, the saturation volume for low and high molecular weight chitosan was 1.3 and 0.45 L and their arsenic removal capacity were 461.8 and 149.5 mg kg-1, respectively. The FT-IR study also confirmed that prepared chitosan’s arsenic removal capacity was higher than that of low and high molecular weight commercial chitosan due to the free amino group.

Arsenic contamination in ground waters is now a worldwide problem and often
referred to as a 21st century calamity (Mohan and Pittman,
2007). Recently, arsenic pollution has been confirmed in the Argentina,
Bangladesh, China, Chile, Canada, India, Japan, Hungary, Mexico, New Zealand,
Poland, Taiwan and USA. Among the 23 countries, Bangladesh and West Bengal (India)
are in the greatest risk for arsenic contamination in groundwater (Rahman
et al., 2005; Van Geen et al., 2003;
Chakraborti et al., 2003; Jain
and Ali, 2002). Several researches revealed that many millions of people
have been exposed to water containing >0.01 mg L-1 As (the WHO guideline
value) drawn from alluvial aquifers in the Bengal Basin (Sengupta
et al., 2008). It is now suspected that more than 100 million people
worldwide ingest excessive amounts of arsenic through drinking water contaminated
from natural geogenic sources (Lenny et al., 2008).

People of Bangladesh and West Bengal are totally dependent on groundwater for
their drinking to household chores. Skin, lung, bladder and kidney cancer as
well as pigmentation changes, skin thickening (hyperkeratosis), neurological
disorders, muscular weakness, loss of appetite and nausea are common diseases
where people consume arsenic contaminated water in long term (Kazi
et al., 2008; Lin et al., 2008; Lubin
et al., 2007; Cantor et al., 2006; Mandal
and Suzuki, 2002). On the other hand, acute poisoning causes vomiting, oesophageal
and abdominal pain and bloody rice water diarrhoea (Duker
et al., 2005; Ng et al., 2003). For
this reason, arsenic free water is the crying need for marginalized people who
can not afford cost of health in Bangladesh and west Bengal.

In recent years, different types of adsorbing materials such as granular ferric
hydroxide (GFH), granular ferric oxide (GFO), activated alumina (AA), modified
activated alumina (MAA) and granular titanium dioxide (TiO2) have
been developed and implemented (Westerhoff et al.,
2006; Bang et al., 2005; Jing
et al., 2005). But very few studies have been done with biopolymer
chitosan. Chitosan, a poly-N-acetylglucosamine, obtained by the deacetylation
of chitin (Crini and Badot, 2008; Orrego
and Valencia, 2008; Dambies et al., 2000).
After cellulose, chitin is the most common polysaccharide found in the nature
extracted from crustacean shells, such as prawns, crabs, insects and shrimps
is a white, hard, inelastic, nitrogenous polysaccharide (Xu
et al., 2008; Xu-fen et al., 2007;
Rinaudo, 2006). Some recent research divulged that natural
biopolymers are industrially attractive because of their capability of lowering
transition metal-ion concentration to parts per billion concentrations. Chitin
and chitosan are considered as natural polymers which have excellent properties
such as biocompatibility, biodegradability to harmless products, nontoxicity,
physiological inertness, antibacterial properties, heavy metal ions chelation,
gel forming properties and hydrophilicity and remarkable affinity to proteins
(Krajewska, 2004; Ravi Kumar, 2000). In addition, Chitin
and chitosan are of commercial interest due to their high percentage of nitrogen
(6.9%). Amine and hydroxyl groups on their chemical structures act as chelation
sites for metal ions making them useful chelating agent.

Adsorption techniques are widely used to remove certain classes of pollutants
from waters, especially those that are not easily biodegradable (Crini,
2006). Adsorption is evolving as a front line of defense because of its
simplicity, ease of operation and handling, regeneration capacity and sludge
free operation (Thirunavukkarasu et al., 2003;
Nurul et al., 2006). Selective adsorption utilizing
biological materials, mineral oxides, activated carbons, or polymer resins,
has generated increasing excitement in removing trace element from contaminated
water (Dambies et al., 2002). In particular, chitosan
can be used as a promising adsorbent for arsenic removal from contaminated ground
water as inorganic forms of arsenic most often exist in water supplies. Two
forms are common in natural waters: arsenite and arsenate referred to as arsenic
(III) and arsenic (V). The present research project is a part of our searching
for better and nature based adsorbent that can successfully remove arsenic and
reduces the cost of getting clean water for poor people in Bangladesh. Particularly,
this project investigated the performance of prepared and commercial high and
low molecular weight chitosan in removing arsenic from contaminated water in
laboratory condition.

MATERIALS AND METHODS

Sample collection: The present study was carried out from February, 2006 to November, 2007 and crab shell was collected from Bio-Chemical and Seafood Export Co., Dhaka, Bangladesh. Low and High molecular weight commercial chitosan were obtained from Marina Chemicals, Dhaka, Bangladesh and used as received throughout this study without any preliminary purification and further modification.

Isolation of chitin from crab shells: Dehooded crab shells was collected,
dried, crushed and decalcified by treatment with 10% HCl, the acid being changed
everyday. The dorsal cover of the shell was peeled off on the third day. Its
inner layer was removed by rubbing it away with the fingers. Thereafter, the
rest of bone was broken into smaller bits. Decalcification was complete in about
four days which can be represented in the following reaction.

2HCl+CaCO3 = CO2+Ca2++2Cl–+H2O

The resulting chitin protein complex of the dorsal cover was deproteinized by the treatment of l0% (w/v) NaOH at 103 to 105°C in an autoclave. The septa region was deproteinized in six hour treatments under similar conditions.

Preparation of chitosan from chitin: Chitin shells, collected from crab shell were dried and again crushed and boiled successively with very dilute HCl for several hours and then it was filtered in a Buchner funnel. The solid was added to sodium hydroxide (20% aqueous solution) and refluxed for four hours and was filtered. The reaction mass was finally added to the deionized water and was again boiled for several hours. After cooling and washing, it was finally dried at 105°C. The powder thus obtained was boiled with 3 N acetic acid and the solution was cooled and filtered. The resulting slurry was neutralized with 15% KOH solution in a large beaker and the precipitate was then filtrated and thoroughly washed with hot water and deionized water. This resulting chitosan precipitates was dried at 105°C and crushed to optimum particle size (100-200) mesh. The IR spectrum of prepared chitosan was taken in KBr disc.

Column preparation: Three columns were made with 5 g uniformly grained prepared chitosan, low and high molecular weight commercial chitosan that collected from Marina Chemicals, Dhaka, Bangladesh and the prepared 10 mg L-1 As3+/As5+ solution with deionized water was passed through the columns until the break through volume as well as saturation volume of the three materials was reached. Water samples that passed through the columns were collected in the sample bottles after several time intervals. The flow rates of the columns were measured and it was range 3-3.5 mL per minute, respectively. All columns were made by Pyrex glass of length 47 cm and diameter 2 cm and length of all the column materials was 5 cm.

Arsenic detection method: Arsenic analysis was carried out using SHIMADZU model AA-6800 Atomic Adsorption Spectrophotometer (AAS) in Bangladesh Atomic Energy Commission, Dhaka. The AAS was calibrated for the arsenic by running different concentrations of standard solutions. Average values of three replicates were taken for each determination. Analytical conditions for the measurement of arsenic in water using AAS are follows: wavelength (nm) 193.7, Slit (nm) 0.5, lamp current (mA) 12, calibration range (μg L-1) 0.001-0.006 and detection limit (μg L-1) 0.003.

RESULTS AND DISCUSSION

To prepare chitosan it is required to isolate chitin in its pure form. Here, we obtained chitin form crab shells that contain calcium and protein at a large scale. Therefore, extracted chitin remains covered with calcium and even after decalcification and deproteinization treatment several times with HCl and NaOH in reflux condition. It was estimated from the study that about 0.2705 g calcium remained per gram of crab shells.

The IR spectra of chitosan were taken and compared with the IR spectra of chitin. The Infrared spectra clearly showed a marked change due to the removal of acetyl groups from the amino nitrogen. In the IR of chitin and chitosan all the stretching frequencies for the different functional groups were almost same. But the stretching frequency of C = O was missing in the spectrum of chitosan.

Secondary amide in the solid state usually showed the C = O absorption near
1640 cm-1. In the spectrum of chitin there were two strongly perpendicular
bands near the frequency at 1652 cm-1. According to the spectrum
of chitosan which was obtained from deacetylation of the chitin, the C = O stretching
frequency at 1640 cm-1 was missing but two bands occurred at 1625
cm-1 that is also supported by the study by Shin
et al. (2001). This band is due to the antisymmetric deformational
vibration due to the formation -NH3+ because chitin is
dissolved in HCl during the reaction. The band appearing at 1521 cm-1
may be assigned to the symmetric -NH3+ deformational mode.
In addition, the IR spectrum of the prepared Chitosan was confirmed from pure
Chitosan. The physical and chemical property of the prepared chitosan was compared
with the original (97% pure) chitosan and it was observed that this pure chitosan
was inactive in both acid and base but the prepared chitosan was slightly soluble
in acid and it was basic impurity. Here, CaCO3 was present in a large
scale.

To investigate the arsenic removal efficiency of prepared crab shell chitosan,
10 mg L-1 of arsenic solution (As3+/As5+, 1:1)
was passed through the chitosan packed column (5 g) and it was found that the
average arsenic adsorbing capacity of prepared chitosan was 52%. The amount
of arsenic passed through the prepared chitosan composite is 12008.077 mg kg-1
and the amount of arsenic absorbed 6244.2 mg kg-1 in Table
1. The earlier studies by Dambies et al. (2002)
and Chen et al. (2008) revealed that modified
chitosan gel beads prepared by the molybdate adsorption and coagulation methods
showed relatively better performance to remove both states of arsenic though
it was more efficient to remove As (V) than As (III). Though the mechanism of
the adsorption was not clear enough but it was suggested that the sorption mechanism
is a complexation between arsenate ions and molybdate ions.

However, the arsenic removing performance of the commercial low and high molecular weight chitosan was relatively much lower than that of prepared chitosan. The amount of arsenic passed through the low molecular weight chitosan (LMWC) was 1721.48 mg kg-1 and the adsorption was 464.8 mg kg-1 in Table 2. Similarly, the amount of arsenic passed through the high molecular weight commercial chitosan was 711.90 mg kg-1 and the amount of arsenic absorbed 149.5 mg kg-1 in Table 3. The FT-IR spectra of the low and high molecular weigh commercial chitosan offered obscure information about the groups, it may be due to the presence of impurity.

To estimate the each adsorption amount of the three chitosan materials, influent
(Co) and effluent (Ce) concentration were calculated and it was observed that
initially the adsorption amount of the prepared chitosan was expectedly high
and it was gradually decreased over time. However, the adsorption amount was
not uniformly decreased with time and a probable reason was that the passing
rate of the prepared arsenic solution through the column was not same. Surface
area and contact time also played a vital role for the adsorption of arsenic
in prepared and commercial chitosan.

The effect of flow rate was more significant for prepared chitosan than that
of high and low molecular weight commercial chitosan. About 48 h was required
to reach 100% breakthrough of prepared chitosan (Fig. 1) whereas
2.5 h was required for both high and low molecular weight commercial chitosan
(Fig. 2-3). This study revealed that the
prepared chitosan required much more time to reach 100% breakthrough point than
that of the chitosan bead study by Chen and Chung (2006).

The use of polymer as adsorbents and in particular chitosan is an enormous
complicating factor. The shape of the uptake isotherms (Fig. 1-3)
showed that the uptake process is a complex one. Simple ion adsorption on the
chitosan surface does not appear to be the dominant mechanism as is inferred
from literature. It is concluded from the previous study where under moderate
magnification, metal containing aggregates were observed on the polymer. So,
a possible uptake mechanism is the formation of metal-containing nodules on
the polymer surface.

Absorption presumably by diffusion of metal ions into the polymer is also playing
a part in the total process. Further chitosan embedded or laced with calcium
carbonate in the composite materials may create some cryptand sites of right
size so that some metals are simply caged at those sites. Thus a combination
of nodular formation, cryptand site formation, ion adsorption and ion absorption
account for the total uptake. The greater uptake is attributed due to the free
amino group of chitosan having its lone pair electrons can act as a specific
chemical bonding sites for arsenic ions capable of forming complex ions. Research
by Guibal (2004) also confirmed that metal cations can
be adsorbed by chelation on amine groups of chitosan in near neutral solutions.

CONCLUSION

Overall, prepared chitosan from crab shell exhibited efficient arsenic removal in adsorption filtration methods whereas low and high molecular weight commercial chitosan showed least performance due to impurity and incomplete deacetylation process. From these findings, it is suggested that prepared crab shell chitosan can be used as a promising bioadsorbent for removing arsenic.

ACKNOWLEDGMENT

We would like to thanks Dr. Syed Safiullah, Professor, Department of Chemistry, Jahangirnagar University, Bangladesh, for his sincere help in this research project.